The present invention relates to transdermal or interdermal drug delivery devices for delivering a liquid drug to a subject via the subject's skin. The invention is particularly useful with respect to the drug delivery device described in our U.S. Pat. No. 5,156,591, and is therefore described below with respect to that device, but it will be appreciated that the invention could advantageously be used in other types of drug delivery devices.
Our U.S. Pat. No. 5,156,591 describes a transdermal drug delivery device which delivers a drug to the subject by means of an electrically-induced mass transfer phenomenon called iontophoresis. This process for drug delivery has recently become of great interest, and many such transdermal delivery devices have been described in the patent literature, including U.S. Pat. Nos. 4,164,226, 4,640,689, 4,708,716, 4,752,285, 4,693,711, 5,057,072, U.S. Statutory Invention Registration H516, and European Patent Application Publication 0299631. Other methods of electrically-aided or electrically-controlled transdermal drug delivery devices are described in U.S. Pat. No. 4,886,513, as well as in our prior U.S. Pat. Nos. 5,062,834 and 5,090,963.